Detrital Zircon Geochronology of the Queen Charlotte Group, Haida Gwaii, British Columbia
Bibliographic record
Abstract
Marine clastic strata of the Queen Charlotte Group (QCG), exposed within Skidegate Inlet on Haida Gwaii, British Columbia, Canada, provide a comprehensive stratigraphic record of Cretaceous forearc deposition on the Wrangellia Terrane. These exposures include the Aptian to Campanian Longarm, Haida, Skidegate, Honna, and Tarundl formations. Detrital zircons from these strata provide a unique opportunity to test linkages between the Wrangellia-Alexander, Taku and Yukon-Tanana terranes in the Cretaceous. Twelve samples were collected through the Cretaceous stratigraphic succession and 300 U-Pb measurements were obtained for each sample by LA-ICP-MS. Detrital zircon populations are dominated by two Mesozoic sub-populations with modes at ~150 Ma and ~90 Ma. These ages indicate QCG strata derive predominantly from rocks of the northwest Coast Plutonic Complex (CPC) to the east where rocks of this age are common. A small but consistent Paleozoic (~400 to 430 Ma) population in samples from the Longarm, Haida, Skidegate and Honna formations suggests a linkage to the Alexander Terrane during the Early to Late-Cretaceous. The youngest strata sampled, the Latest Campanian Tarundl Formation, yielded detrital zircons with complex U-Pb systematics indicative of inheritance. Cores from the Tarundl Formation yield dates of 300-400 Ma and 1000-2800 Ma, similar to sedimentary rocks of the Yukon-Tanana Terrane. Zircon rims within the youngest sub-population yield a single age (86.7 ± 1.2 Ma; MSWD 8.0) suggesting the Tarundl Formation derives from a restricted source area and potentially a single magmatic body. The ages of inherited cores indicate this source likely intruded rocks of the Yukon-Tanana Terrane such as the basal Port Houghton assemblage. Maximum depositional ages (MDAs) indicate syn-magmatic sedimentation from the Aptian to Campanian, which is consistent with biostratigraphic age constraints (e.g. McLearn, 1972; Haggart, 1991; Haggart, 2009). However, clustering of the MDA suggests punctuated sedimentation that was likely deposited by migrating channel systems. Detrital zircon ages from rocks of the QCG indicate derivation was from source areas located west of the Coast Shear Zone (CSZ). Therefore, a linkage to sources east of the CSZ is not necessary to explain provenance for the Queen Charlotte Group.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".